Over the past several years, personal desktop computer have made tremendous leaps in capability. However, changing or reconfiguring the hardware usually requires the computer be opened thereby causing some anxiety for the end user. Manufacture of several "add-on" devices, such as scanners, tape machines, CD players, network interfaces have realized that interfacing their product to the computer's parallel port eliminates the need to open the computer. These parallel port add-ons have gained additional functionality with the standardization of a bidirectional parallel port as defined by the IEEE Std 1284-1994 specification entitled IEEE Standard Signaling Method for a Bidirectional Parallel Peripheral Interface for Personal Computers, (Dec. 2, 1994) incorporated herein by reference (herein referred to as IEEE 1284).
Personal desktop computer parallel interface add-ons are becoming more numerous and useful. However, with the present parallel port, the user must keep connecting one and disconnecting another. Some of these add-ons provide a pass-through port connection for connecting a printer. Such a configuration can be seen in FIG. 2. Typically, a second add-on may not be connected to the pass-through port. Such daisy-chain may be possible, however, it may not always work. The parallel port on a personal computer was not designed for daisy-chaining.
An additional problem exists with IEEE 1284 compatible ports. Some printer drivers and their associated status monitors currently lock the parallel port, thereby disallowing any other device access to the port.